1. Field of the Invention
The invention relates to an arrangement for measuring the pulse transmission spectrum of x-ray quanta elastically scattered in a scanning area for containers, comprising a polychromatic x-ray source arranged on one side of the scanning area and a detector arrangement arranged on the other side of the scanning area for measuring the energy of the scattered x-ray quanta as well as a primary ray collimator arrangement and a secondary ray collimator arrangement, allowing passage only of scattered rays within a certain scatter angle range to the detector arrangement, wherein the primary ray collimator arrangement is arranged between the scanning area and the x-ray source and the secondary ray collimator arrangement is arranged between the scanning area and the detector arrangement, and further comprising means for processing the measured signals.
2. Description of the Related Art
Such an arrangement is known, for example, from European patent document EP-B1-360 347.
Moreover, baggage inspection systems are known which operate on the principle of examining with coherent x-rays (coherent x-ray scanning, CXRS), for example, disclosed in European patent document EP-A1-0 556 887. The devices of these systems are based on an arrangement of radiation source and detector in which the primary ray is fixed relative to the other components. In order to be able to analyze a container, such as a piece of baggage or the like, and its contents completely, the entire measuring system must be moved relative to the corresponding part to be examined. The corresponding mechanism is often slow, clumsy, and complicated so that scanning times of 60 seconds are common.
Moreover, the measuring time depends on the power of the x-ray source. In order to provide safe information in regard to the presence of explosives, drugs and the like within the piece of baggage, it is necessary that a certain number of scattered quanta are detected. The higher the power of the x-ray tube, the shorter the required measuring time. The maximum continuous power of a rotary anode tube is approximately 10 kW. This value, in addition to the mechanism, presents a limitation for the minimal scanning time of the piece of baggage which is approximately 1 minute.
The output signals of the detector elements can be processed such as, in particular, disclosed in the German patent application P 41 01 544. This known processing method is therefore not to be explained in detail in this context. It shall only be mentioned that for each detector element one processing channel is provided in which the signal is amplified, digitalized, and supplied to a pulse height analyzer which registers the number of x-ray quanta in the different energy ranges. For each detector element and for each energy range this number is divided by the number of x-ray quanta which have been registered by means of the central detector D0 for the corresponding energy range. This provides the respective energy spectrum for each detector element, independent of the energy distribution of the x-ray quanta emitted by the x-ray source and substantially independent of the weakening of the scattered radiation caused by the object.
X-ray tubes with xe2x80x9cjump focusxe2x80x9d (the focus can jump back and forth, i.e., is deflected) are known in the prior art and are commonly referred to as swept focus or scanning focus; an example is Digi-Ray(copyright) in which the xe2x80x9cinverse geometryxe2x80x9d is preferred. This type of arrangement is called xe2x80x9cinversexe2x80x9d because the traditional functions of x-ray source and detector (i.e., of point detector and extended source) is reversed in this system. The reference Solomom E. G., Wilfly B. P., Van Lysel M. S., Joseph A. W., and Heanue J. A., 1999, Scanning beam digital x-ray (SBDX) system for cardiac angiography, Physics of Medical Imaging SPIE Proc. 3659, 246-257 (Eds. J. M. Boone and J. T. Dobbins) relates to a publication of the company Cardiac Mariners Inc. This company uses an x-ray source with xe2x80x9cjump focusxe2x80x9d for generating blood vessel images, primarily of the heart. Since x-ray sources with scanning beams or xe2x80x9cjump focusxe2x80x9d are disclosed sufficiently in scientific and technical literature with respect to xe2x80x9cinverse geometryxe2x80x9d, they will not be discussed in detail in this context.
It is an object of the present invention to improve the arrangement of the aforementioned kind such that essentially no mechanical movement of the x-ray source is required and, at the same time, an amplification of the power of the x-ray beams is achieved so that a substantial shortening of the scanning or examination duration of the containers within the range of seconds is possible, in particular, for use in airports.
In accordance with the present invention, this is achieved in that the detector arrangement (D1, . . . Dn) is positioned on a Z axis, which simultaneously forms an axis of symmetry about which the secondary ray collimator arrangement extends cylindrically symmetrically, wherein on the Z axis a point 0 is provided which determines the origin of a Cartesian coordinate system with X axis and Y axis, wherein the conveying axis for the container to be examined extends parallel to the Z axis, and in that the primary ray collimator arrangement (P) allows passage only of x-ray beams which are substantially impinging on the point 0, wherein the x-ray source (Q) is arranged behind the primary ray collimator arrangement (P) with an extended anode whose focus position can be electronically controlled about the length of the anode, and wherein the primary ray collimator arrangement (P) and the x-ray source (Q) extend cylindrically symmetrically about the axis of symmetry or linearly parallel to the Y axis in the X-Y plane.
In the CXRS arrangement or device according to the invention, the axis of symmetry, in contrast to all CXRS systems presently known, does not extend through the focus of the x-ray tube or x-ray source. Accordingly, the present invention describes a novel CXRS geometry based on an x-ray tube with xe2x80x9cjump focusxe2x80x9d (swept focus) which is characterized particularly in that mechanical scanning movementsxe2x80x94aside from the required forward movement on a conveyor beltxe2x80x94when examining containers of any kind, in particular, pieces of luggage and the like, are avoided and an x-ray source with great power can be used. Moreover, it is possible to significantly reduce the surface and thus the technical complexity of the detector arrangement which in the known systems represents an important cost factor. Cooling by using the Peltier effect is possible according to the invention so that the use of liquid nitrogen or complex cryogenic generators, as needed in the case of semiconductor detectors, can be avoided.
For a better understanding of the invention, the invention will be explained in the following with the aid of an embodiment. The values in regard to dimensions are given in mm and all angles are given in radian. The invention is not limited to the illustrated and described embodiment but can be adapted within the gist of the present invention.